Today, in optical storing media is widely used the optical reading based on laser beam reflection from reflecting elements of recording track. The track is spiral-shaped and recording/reading head has the special mechanism that follows the spiral in such a way that optical axis of reading lens is aligned with the center of track. A conventional disk (CD, DVD) usually has a single or double-side layer and data capacity of regular single-side DVD does not exceed 4.7 Gb that is not enough for HD TV. Because technological ability is close to limit (the distance between DVD tracks is 0.34 micrometers, and size of reflecting element is 0.34 micrometers), the only way to increase the data capacity is a multi-layer optical disk.
There are number of methods of creating of multi-layer recording by means of writing of layers placed on different depth in the disk, such as, for example, described in U.S. Pat. No. 4,219,704 issued to Russell Aug. 26, 1980. Here, author proposed a general idea of reading of multi-layer disk by means of “selection of one data track for playback accomplished by changing the focus of the light beam from one data layer to another, or by making the data tracks of optically different materials, such as using different color dyes or different photoluminescent materials, and selectively positioning corresponding color filters in front of the light detectors”. In this patent the author does not specify light source of the reading head. The similar idea of multi-layer recordable optical disk is described in U.S. Pat. No. 4,451,915 issued to LaBudde, et al. May 29, 1984.
U.S. Pat. No. 4,908,813 issued to Ojima Mar. 13, 1990 and U.S. Pat. No. 4,973,832 issued to Marchant, et al. Nov. 27, 1990 provide more detailed description of the proposed multi-layer optical disk. In this case, elements of the recorded track contain reflected and transparent parts that allows to laser beam penetrating through upper layer. Laser utilized in the disk reader of this patent emits a number of different wavelengths, wherein single lens having high chromatic aberration focuses laser beam of the first wavelength on the upper layer of the disk and the beam of the second wavelength on the lower layer. Reflected beam is collected by single light sensor. The similar approach is described in U.S. Pat. No. 7,106,664 issued to Hasegawa, et al Sep. 12, 2006. Here, the disk contains number of transparent dielectric layers having different refracting index and different sickness that, according to the authors, allows focusing laser radiation of specific wavelength on the specific layer containing recording track, therefore, according to the authors, providing possibility of multi-layer writing and reading.
Reading head of the existing and proposed in previous patents optical disk readers contains a single or multi-wavelength laser diode mounted directly on the movable head. Such design is suitable for a single-wavelength laser diode only. If the laser diode is a multi-wavelength one (the multi-wavelength light source proposed in mentioned above patents), it can not be properly fit into the reading head because it requires light-separation system sequentially switching the wavelengths; therefore, the head becomes complicated and bulky.
Also, capacity of optical storages is limited by optical resolution that directly depends on wavelength of LD installed in the reading head. The most advanced HD readers, such as BlueRay® HD DVD players utilize short visible (405-nm) wavelength that allows five-time increasing of the disc capacity in comparison with conventional DVD utilizing red (650-nm) LD. Moving in UV region could allow further increasing of optical storage capacity. The main obstacle here is absence of UV LD, which can be directly installed in the reading head. There number of UV lasers that can be used in such storages, but its sizes do not allow directly fitting them in the head. One of the most advanced lasers emitted short UV is 4-th harmonic DPSS laser emitting 266-nm wavelength. Utilization of such laser could additionally increase capacity in about 4 times. To realize this possibility, the author of the present invention proposes a fiber-optic (FO) connection between the laser and the head. In this case the laser can be installed in any convenient place of player/recorder. To keep low divergence of the light beam, the fiber-optical line is a single-mode one.
Another problem of optical storages is a high preciseness of the mechanism positioning the head about the track, which can keep position of the light beam on disk's track. Also, it has to be rigid enough to keep position under some mechanical effects, such as shock and vibration. It becomes even more important for HD recorders/players. There are a number of patents where the authors proposed methods and apparatus that, according to them, can solve this problem. In the U.S. Pat. No. 4,198,657 issued to Kanamaru Apr. 15, 1980 the author propose movable mirror to compensate light spot variation caused the mentioned above effects. Obvious disadvantage of the solution proposed in the U.S. Pat. No. 4,198,657 is a mechanical element—a movable mirror—that requires an actuator and has all disadvantages of mechanical moving elements, such as low speed, overshooting, etc. Another solution was proposed in the U.S. Pat. No. 5,329,507 issued to Nelson et al. Jul. 12, 1994. Here the author proposed an optic waveguides having electro-optical property that allows deflecting the light coming from the guides so changing position of light spot on the disk. Such solution can provide very small deflection angle, therefore it can not be successfully utilized to keep light on the track.
To solve this problem, the author of the present invention proposes an acousto-optical scanner built in a reading/recording head that allows light beam following the track and provide anti-skipping ability.
The present invention alleviate the disadvantages of the previous art by means of utilization of the novel fiber-optic (FO) and acousto-optic (AO) technology that allows precisely positioning the light spot on disk's track, providing fast anti-skipping ability and security of disk information. Also, it allows installing the laser and light-separating filters in any convenient place of the disk reader/recorder, wherein they are optically connected to movable head via a single-mode FO line. Such solution allows significantly increasing disk capacity by means of utilization of short-wavelength UV lasers, which can not be used in conventional optical reading/recording devices, because, despite its small size, it can not be directly built in the reading head.